The present invention relates to an optical system for alignment of such with associated electrical and optical components.
Many devices, including semiconductor devices or other such similar electrical or electronic components, require heatsinking and cooling due to their high level generation of heat during their operation. If not properly dissipated, the generated heat may adversely affect the resulting operating conditions of the device as well as affect the prealignment of optical components in the device.
Heat dissipating devices, such as semiconductor light sources, laser diodes, MOPA devices, laser diode arrays, single or multiple laser bars, optical transceivers or optical integrated circuits, semiconductor chips or other integrated circuit chips, hereinafter collectively referred to as "semiconductor device(s)", are being designed at increasingly larger power levels so that, without adequate cooling of these devices during their operation, they would self-destruct in a relatively short period of time. Presently, the cooling is effectively carried by mounting the laser diode package on a heatsink which is mounted on a microchannel fluid cooler or on an thermal electric cooler. An example of the former is shown in U.S. Pat. No. 5,107,091 and an example of the latter is shown in U.S. Pat. No. 5,270,869. While these heat dissipation techniques provide for increased efficient means of carrying away heat dissipated from these devices, there is a problem of bulkiness of the cooler for modern applications of these devices as well as subsequent misalignment of the mounted semiconductor device relative to associated electrical and optical components, such as lenses, waveplates, optical fibers, which are initially aligned in proper axial alignment with the output provided from the semiconductor device. Over time, misalignment can occur due to warpage of the heatsink supporting the semiconductor device.
As indicated above, one of the present key technologies in semiconductor device packaging is the employment of a heatsink upon which the semiconductor device and its associated submount is mounted, and the mounting of the heatsink directly onto a thermal electric cooler. A specific example of a typical small package configuration is the employment of a copper heatsink in the form of a copper bar soldered directly to a ceramic thermal electric cooler. However, as the package configuration increases due to larger semiconductor devices in both physical size and power requirements, the package size correspondingly increases resulting in larger mismatches in thermal expansion between copper and ceramic materials. The consequence is that substantial stress deflection and warpage of the heatsink causes potential separation of the heatsink from the cooler. Also, even without separation, warpage occurs resulting in misalignment of the initially preset alignment of the semiconductor device with its associated electrical and optical components. Also, the stress cause by the thermal mismatch of materials due to their different thermal coefficients may result in catastrophic failure of the thermal electric cooler.
A particular example of heat dissipation resulting in substantial heatsink stress deflection is in connection with a fiber coupled MOPA device mounted on a copper heatsink block soldered to a ceramic thermal cooler. An example of such a product is the 1 watt CW single mode MOPA laser diode, SDL-5762 package, manufactured and sold by SDL, Inc., the assignee herein. Heatsinking in such a package can be of considerable concern because of the significant size of the required cooler, e.g., 1" by 2". Submicron alignment tolerances of aligned components in the package (whether such components may be mounted partly on or off the heatsink), with the output provided from the MOPA device are apt to become significantly misaligned due to heatsink stress deflection caused by thermal expansion differences between the copper heatsink and the ceramic cooler. This stress deflection is illustrated in FIG. 1 showing a computer simulation of a solid copper heatsink block 10 soldered to a 3 mm thick ceramic plate 12 of the type employed relative to a thermal electric cooler. MOPA device 16 is shown mounted on copper submount 14 which, in turn, is mounted on heatsink block 10. As shown in FIG. 1, when heatsink block 10 is heated, there results significant bowing and warpage of heatsink block 10 due to the differences in thermal transfer coefficients of copper block 10 and ceramic plate 12. A few degrees change in temperature will cause substantial misalignment. The resulting stress deflection of heatsink 10, particularly as shown the forward end 18 of the heatsink, for example, may be several microns. This amount of stress deflection would result in substantial misalignment of the output of MOPA device 16 with associated aligned components, such as an input end of an aligned optical fiber, which is entirely unacceptable.
It is an object of this invention to provide an optical system for alignment of electrical and optical components relative to a heatsink so that precision alignment with maximum coupling efficiency to a optical transmission medium is achieved.